Pregnancy diagnosis in dairy cattle enables planned breeding in dairy management, and allows early detection and treatment of reproductive disorders, and it is important to perform the diagnosis at an early stage of pregnancy in order to improve the conception rate after intrauterine insemination and prevent infertility. As a result of the diagnosis, if pregnancy is detected, adequate care during pregnancy and a hygienic conditions will be provided to prevent abortion early in the pregnancy and help cows to give birth to healthy calves. Otherwise, if pregnancy is not detected, the cause of non-pregnancy should be found to take proper actions, and intrauterine insemination (Artificial insemination) may be tried as soon as possible to increase the reproductive efficiency of the cows. Accordingly, dairy cattle pregnancy should be diagnosed at an early stage of pregnancy if possible. Moreover, the diagnosis should not affect pregnant cattle and their fetuses, the diagnostic method should be easy to perform at low cost and livestock farms should be easy to perform this technology.
Pregnancy diagnosis in cattle methods currently in use include rectoscopy, ultrasonic diagnosis, and a pregnancy diagnosis method using a diagnostic kit that uses changes in hormone concentration in blood.
The rectoscopy is a method for detecting pregnancy by observing changes in reproductive organs, for example, womb size, waving feeling, position, fetal membranes, corpus luteum, fetus, placental growth stimulation, or uterine artery hypertrophy, through rectal examination. The ultrasonic pregnancy diagnosis, as a rule, uses a linear type probe of 5.0 MHz or 7.5 MHz attached to an ultrasonic diagnostic apparatus. With this method, a round or elliptical embryo sac that appears to be black can be observed in the uterine horn around 22 days of pregnancy. However, it is desirable to perform diagnosis after 27 days of pregnancy. Amniotic fluid appearing to be black is observed in the uterine horn around 30 days of pregnancy, and the fetus looks like a white processus. It is possible to estimate how many days old the fetus by measuring the length of the fetus and the size of each structure, and it is also possible to identify the sex of the fetus by detecting the positions of reproductive organics between 60 and 120 days of pregnancy. The risk of miscarriage is very low because the test is done by moving the probe over the womb without pulling the womb.
The pregnancy diagnostic kit using changes in hormone concentration in blood was developed with the focus on the fact that the progesterone concentration in the blood or milk from nonpregnant cows is lower than that of pregnant cows. If a cow is pregnant, the corpus luteum grows into persistent corpus luteum and is involved in the maintenance of the pregnancy. Therefore, pregnant cows have a higher level of progesterone (above 3 to 4 ng/ml) than nonpregnant cows (1 ng/ml or so) due to the effects of progesterone released from the persistent corpus luteum.
The rectoscopy may be used for diagnosis after 30 to 40 days of pregnancy. As the diagnostic accuracy varies according to the degree of training of vets, a proper time for diagnosis should be chosen according to the degree of skillfulness of vets. Moreover, a report showed that 10% of fetuses from cattle were stillborn due to early absorption before 150 days of pregnancy when the diagnosis using rectoscopy had been performed around 35 to 41 days of pregnancy, and 8% of cattle, on average, on which an early pregnancy diagnosis was performed by rectoscopy miscarried around 60 days of pregnancy. This reveals the drawback that the sooner the pregnancy diagnosis is made, the higher the risk of early death of fetuses.
In the ultrasonic pregnancy diagnosis, amniotic fluid and a fetus can be seen directly through the screen of an apparatus. Thus, it is an accurate pregnancy diagnosis method, but limitations on the use of this method in livestock farms because an expensive ultrasonic diagnostic apparatus are required.
In the pregnancy diagnosis using a diagnostic kit, the accuracy is not more than 70 to 80%; the reason of which is, because cows show high levels of progesterone if they have reproductive disorders caused by ovarian diseases or uterine diseases, resulting in a high rate of misidentification.
Currently, a number of pregnancy-associated proteins from livestock have been reported: equine chorionic gonadotropin (ECG) is used for pregnancy diagnosis in horses, bovine placental lactogen (bPL), pregnancy specific protein-B (PSPB), pregnancy serum protein-60 (PSP-60) and bovine pregnancy-associated glycoprotein (bPAG) are used for pregnancy diagnosis in cattle, and progesterone in milk or serum is also used. However, in the case of pregnancy diagnosis using the pregnancy-associated proteins and progesterone, the misidentification rate of negative and positive specimen is relatively high, and hence the accuracy of a pregnancy test is not high, thus leading to low practicability. Consequently, there is a need for the development of a new method for making accurate diagnosis of cattle pregnancy more easily and quickly at an early stage.